This invention is in the field of industrial water systems. Specifically, this invention is in the field of monitoring and controlling soluble hardness in water in industrial water systems. This invention also is in the field of determining whether Total Hardness is due to the presence of calcium or magnesium or some combination of calcium and magnesium.
xe2x80x9cTotal Hardnessxe2x80x9d is a term that refers to the amount of calcium and magnesium cations present in water and is usually expressed as ppm CaCO3 equivalents. xe2x80x9cSoluble hardnessxe2x80x9d refers to soluble Ca+2 and Mg+2 cations present in water. xe2x80x9cParticulate hardnessxe2x80x9d or xe2x80x9ccolloidal hardnessxe2x80x9d refers to hardness that is insoluble (or xe2x80x9cnon-solublexe2x80x9d). Insoluble hardness can usually be converted to soluble hardness by treating the water with acid and heat. Soluble hardness concentrations in the water of most industrial water systems can range from less than about 1 ppm to about several thousand ppm.
The presence of soluble hardness in industrial waters typically leads to precipitation of those cations as scale on heat transfer surfaces of industrial process equipment. The presence of scale is detrimental to many individual units of industrial process equipment as well as to the industrial water system itself. Systems affected negatively by scale deposits include boilers, multi-stage evaporators, cooling water heat exchangers, cooling towers, hot water heaters, continuous casters, heat recovery steam generators, pipe surfaces and any other heat transfer surfaces of equipment present in industrial water systems.
Scale deposits are undesirable because deposited scale can cause impedance of flow, loss of cooling and reduced heat transfer capability, and xe2x80x9cunder depositxe2x80x9d corrosion problems. Under deposit corrosion problems are caused when chemical species which lead to corrosion (such as hydroxyl ions) concentrate to a point significantly higher than that found in the boiler bulk water. These high concentrations are more corrosive and can lead to tube failure.
Scale deposits are also undesirable because they can provide an environment that allows microbiological attachment and growth leading to microbiological induced corrosion problems. These undesirable situations can ultimately result in equipment failure such as boiler tube ruptures and heat exchanger failures, and unscheduled outages where it is not possible to operate the equipment. All of these undesirable situations can lead to a loss of capital equipment with resultant loss of production time and money.
The process by which soluble species precipitate from the water in a boiler onto a surface is usually referred to as xe2x80x9cscalingxe2x80x9d. The process by which insoluble species suspended in water are xe2x80x98left behindxe2x80x99 and adhere to surfaces is usually referred to as xe2x80x9cdepositionxe2x80x9d and the insoluble species that adhere to surfaces are typically referred to as a xe2x80x9cdepositxe2x80x9d. In a boiler, this is of most concern at the areas where a wet/dry interface is present. This wet/dry interface is where the steam bubble is initiated, grows, and then detaches from the surface. Insoluble matter can collect and adhere at the interface of the bubble to the surface as it grows. With detachment of the steam bubble, the insoluble matter may adhere to the surface forming a deposit. These deposits are unwanted as their presence disrupts the heat transfer from the surface to the water.
It is common to monitor the soluble hardness in the water of an industrial water system and to treat industrial water systems such that soluble hardness does not scale and insoluble hardness does not deposit. The treatment products used to treat water are many and varied. xe2x80x9cScale inhibitorsxe2x80x9d are typically defined as chemical treatments that are added to water which reduce or eliminate the scaling process. xe2x80x9cDispersantsxe2x80x9d are typically defined as chemical treatments that are added to water to reduce or eliminate the accumulation of insoluble species as deposits on surfaces. When the insoluble matter is dispersed, it typically is not able to deposit. If the insoluble matter remains dispersed then it can be xe2x80x9ccarried awayxe2x80x9d in the natural flow patterns of the industrial water system.
Treatment products for industrial waters to remove, inhibit or control the detrimental effects of scale and deposits caused by the presence of soluble and insoluble hardness present in said waters are well known. Chemical treatment methods useful to treat water for undesirable hardness, based on soluble hardness, include such methods as coagulation, flocculation, precipitation, chelation, sequestration, complexation, dispersion and crystal modification. Treatment products for use in these chemical treatment methods include
a) anionic polymer that can effectively complex with magnesium; these anionic polymers include polyacrylates, polymethacrylates and acrylate styrene sulfonate copolymers;
b) chelants such as ethylenediaminetetraacetic acid, nitrilotriacetic acid, 1-hydroxyethylidene-1,1-diphosphonic acid and hexamethylenediaminetetra methylene phosphonic acid;
c) inorganic phosphates and organic phosphates such as hexametaphosphate, tripolyphosphate and ortho phosphate;
d) polyphosphonates;
e) natural and synthetic cationic polymers such as lignins, lignosulfonates, tannins, poly peptides, polyamines, quaternary amines, celluloses, starches, polymaleic anhydrides and polyvinyl sulfonates;
f) inorganic carbonates and organic carbonates;
g) surfactants; and
h) mixtures thereof, and
i) known salts thereof.
There are industry standards for hardness in the water of industrial water systems. The American Society of Mechanical Engineers (ASME) has published a consensus on operating practices for the control of boiler feedwater and boiler water chemistry in modern industrial boilers. The ASME along with other organizations such as the Electric Power Research Institute (xe2x80x9cEPRIxe2x80x9d), British Boiler Manufacturers, Japanese Boiler Manufactures, German (VGB) boiler feedwater and boiler water guidelines for boiler systems, specify the acceptable maximum amount of hardness in feedwater to minimize the potential for hardness scale deposit problems that can lead to boiler failures.
The amount of soluble hardness present in industrial waters can change rapidly. If this change in soluble hardness goes unnoticed and the amount of treatment product for soluble hardness is unchanged in the water, the change in soluble hardness will result in under dosing or overdosing of the treatment products that are used to control, inhibit or eliminate the detrimental scaling of soluble hardness and depositing of insoluble hardness.
There are a number of known methods to measure and monitor soluble hardness in industrial waters. Some of these known methods include using sophisticated, time-consuming and expensive instrumentation such as Atomic Absorption Spectrophotometers and Inductively Coupled Argon Plasma Emission Spectrophotometers. Colorimetric methods include visual as well as instrumentation methods. Colorimetric methods that do not require expensive instrumentation include titration techniques that use indicator dyes sensitive to hardness which change color to the naked eye in the presence (or with some dyes, in the absence) of hardness. The majority of these known methods are subject to interferences, are known to be time consuming and the visual calorimetric methods can be very subjective based on subtle-to-the-eye distinctions in color changes.
It would be desirable to have a relatively inexpensive, reliable, non-colorimetric method for determining the level of soluble hardness in the water of an industrial water system. It would also be desirable to have a method to determine what part of the soluble hardness is attributed to calcium and what part of the soluble hardness is attributed to magnesium.
The first aspect of the instant claimed invention is a method of determining the amount of soluble hardness in the water of an industrial water system comprising the steps of:
1) providing an industrial water system;
2) providing a Compound, wherein said Compound is selected from the group of chemicals that develop a separate detectable fluorescent signal in the presence of soluble hardness;
3) extracting a sample of water from the industrial water system and determining whether the sample of water is at or below the maximum temperature of operability of said Compound, and if the sample of water is above the maximum temperature of operability of said Compound, then cooling said sample of water until the temperature of the sample of water is at or below the maximum temperature of operability of said Compound;
4) measuring the pH of the sample of water and determining whether the pH is between about 7.5 and about 13.5 and if the pH is not between about 7.5 and about 13.5, adjusting the pH of the sample of water such that the pH is between about 7.5 and about 13.5;
5) adding to said sample of water from about 1 ppb to about 3,000 ppm of said Compound;
6) providing a fluorometer;
7) using said fluorometer to measure the separate detectable fluorescent signal of said Compound in said sample of water; and
8) using said separate detectable fluorescent signal to determine the amount of soluble hardness in said sample of water.
The second aspect of the instant claimed invention is a method of determining the amount of soluble hardness in the water of an industrial water system comprising the steps of:
1) providing an industrial water system wherein the pH of the water in said industrial water system is between about 7.5 and about 13.5;
2) providing a Compound, wherein said Compound is selected from the group of chemicals that develops a separate detectable fluorescent signal in the presence of soluble hardness;
3) adding to the water of the industrial water system from about 1 ppb to about 3,000 ppm of said Compound, wherein said Compound is added to the water of the industrial water system at a point where the water is at or below the maximum temperature of operability of said Compound;
4) providing a fluorometer;
5) using said fluorometer to measure the separate detectable fluorescent signal of said Compound in said water of said industrial water system; and
6) using said separate detectable fluorescent signal to determine the amount of soluble hardness in said water of said industrial water system.
The third aspect of the instant claimed invention is a method of determining whether the appropriate level of treatment product has been added to the water of an industrial water system comprising the steps of:
1) providing a treatment product, wherein said treatment product comprises scale inhibitor or dispersant or both, and an inert tracer in known proportions;
2) providing an industrial water system;
3) adding said treatment product to the water of said industrial water system;
4) providing a Compound, wherein said Compound is selected from the group of chemicals that develop a separate detectable fluorescent signal in the presence of soluble hardness;
5) extracting a sample of water from the industrial water system and determining whether the sample of water is at or below the maximum temperature of operability of said Compound, and if the sample of water is above the maximum temperature of operability of said Compound, then cooling said sample of water until the temperature of the sample of water is at or below the maximum temperature of operability of said Compound; wherein said sample of water is extracted from the industrial water system at a point where the water in the industrial water system has not had a treatment product added;
6) measuring the pH of the sample of water and determining whether the pH is between about 7.5 and about 13.5 and if the pH is not between about 7.5 and about 13.5, adjusting the pH of the sample of water such that the pH is between about 7.5 and about 13.5;
7) adding to said sample of water from about 1 ppb to about 3,000 ppm of said Compound;
8) providing at least one fluorometer;
9) using said fluorometer to measure the separate detectable fluorescent signal of said Compound in said sample of water;
10) using said separate detectable fluorescent signal to determine the amount of soluble hardness in said sample of water; and
11) increasing the feed rate of treatment product if step 10) shows there is an unacceptable level of soluble hardness present in the water and decreasing or maintaining the feed rate of treatment product if step 10) shows that an unacceptable level of soluble hardness is not present in the sample of water; wherein the amount of treatment product being fed into the water is verified by
a) measuring the fluorescent signal of the inert tracer in said treatment product to determine how much inert tracer is present in the water; and
b) using the amount of inert tracer present to determine the amount of treatment product that is being fed into the water.
The fourth aspect of the instant claimed invention is a method of determining whether the appropriate level of treatment product has been added to the water of an industrial water system comprising the steps of:
1) providing a treatment product, wherein said treatment product comprises scale inhibitor or dispersant or both, and an inert tracer in known proportions;
2) providing an industrial water system wherein the pH of the water in said industrial water system is between about 7.5 and about 13.5;
3) adding said treatment product to the water of said industrial water system;
4) providing a Compound, wherein said Compound is selected from the group of chemicals that develops a separate detectable fluorescent signal in the presence of soluble hardness;
5) adding to the water of the industrial water system from about 1 ppb to about 3,000 ppm of said Compound, wherein said Compound is added to the water of the industrial water system at a point where the water is at or below the maximum temperature of operability of said Compound;
6) providing at least one fluorometer;
7) using said fluorometer to measure the separate detectable fluorescent signal of said Compound in said water of said industrial water system; wherein the measurement takes place at a point where the water in the industrial water system has not had a treatment product added;
8) using said separate detectable fluorescent signal of said Compound to determine the amount of soluble hardness in said water, increasing the feedrate of treatment product if step 7) shows there is an unacceptable level of soluble hardness present in the water and decreasing or maintaining the feed rate of treatment product if step 7) shows that an unacceptable level of soluble hardness is not present in the water; wherein the amount of treatment product being fed into the water is verified by:
a) measuring the fluorescent signal of the inert tracer in said treatment product to determine how much inert tracer is present in the water; and
b) using the amount of inert tracer present to determine the amount of treatment product that is present in the water.
The fifth aspect of the instant claimed invention is a method of determining whether the appropriate level of Selected Treatment Product has been added to the water of an industrial water system comprising the steps of:
1) providing a Selected Treatment Product, wherein said Selected Treatment Product comprises a Selected Scale Inhibitor or Selected Dispersant or both, and an inert tracer in known proportions;
2) providing an industrial water system;
3) adding said Selected Treatment Product to the water of said industrial water system;
4) providing a Compound, wherein said Compound is selected from the group of chemicals that develop a separate detectable fluorescent signal in the presence of soluble hardness;
5) extracting a sample of water from the industrial water system and determining whether the sample of water is at or below the maximum temperature of operability of said Compound, and if the sample of water is above the maximum temperature of operability of said Compound, then cooling said sample of water until the temperature of the sample of water is at or below the maximum temperature of operability of said Compound;
6) measuring the pH of the sample of water and determining whether the pH is between about 7.5 and about 13.5 and if the pH is not between about 7.5 and about 13.5, adjusting the pH of the sample of water such that the pH is between about 7.5 and about 13.5;
7) adding to said sample of water from about 1 ppb to about 3,000 ppm of said Compound;
8) providing at least one fluorometer;
9) using said fluorometer to measure the separate detectable fluorescent signal of said Compound in said sample of water;
10) using said separate detectable fluorescent signal to determine the amount of soluble hardness in said sample of water; and
11) increasing the feed rate of Selected Treatment Product if step 10) shows there is an unacceptable level of soluble hardness present in the water and decreasing or maintaining the feed rate of Selected Treatment Product if step 10) shows that an unacceptable level of soluble hardness is not present in the sample of water; wherein the amount of Selected Treatment Product being fed into the water is verified by
a) measuring the fluorescent signal of the inert tracer in said Selected Treatment Product to determine how much inert tracer is present in the water; and
b) using the amount of inert tracer present to determine the amount of Selected Treatment Product that is being fed into the water.
The sixth aspect of the instant claimed invention is a method of determining whether the appropriate level of Selected Treatment Product has been added to the water of an industrial water system comprising the steps of:
1) providing a Selected Treatment Product, wherein said Selected Treatment Product comprises Selected Scale Inhibitor or Selected Dispersant or both, and an inert tracer in known proportions;
2) providing an industrial water system wherein the pH of the water in said industrial water system is between about 7.5 and about 13.5;
3) adding said Selected Treatment Product to the water of said industrial water system;
4) providing a Compound, wherein said Compound is selected from the group of chemicals that develops a separate detectable fluorescent signal in the presence of soluble hardness;
5) adding to the water of the industrial water system from about 1 ppb to about 3,000 ppm of said Compound; wherein said Compound is added to the water of the industrial water system at a point where the water is at or below the maximum temperature of operability of said Compound;
6) providing at least one fluorometer;
7) using said fluorometer to measure the separate detectable fluorescent signal of said Compound in said water of said industrial water system;
8) using said separate detectable fluorescent signal of said Compound to determine the amount of soluble hardness in said water, increasing the feedrate of Selected Treatment Product if step 7) shows there is an unacceptable level of soluble hardness present in the water and decreasing or maintaining the feed rate of Selected Treatment Product if step
7) shows that an unacceptable level of soluble hardness is not present in the water; wherein the amount of Selected Treatment Product being fed into the water is verified by:
a) measuring the fluorescent signal of the inert tracer in said Selected Treatment Product to determine how much inert tracer is present in the water; and
b) using the amount of inert tracer present to determine the amount of Selected Treatment Product that is present in the water.
The seventh aspect of the instant claimed invention is a method of determining whether soluble hardness is calcium or magnesium comprising the steps of
(a) providing a sample of a fluid that is believed to contain both calcium and magnesium;
(b) determining the wavelength of the isosbestic point of Plasmocorinth B in said fluid by measuring the absorbance of the same fluid containing the same amount of Plasmocorinth B and fixed Total Hardness while varying the relative amounts of magnesium and calcium in the Total Hardness, and plotting the absorbance versus wavelength; wherein the isosbestic point is the wavelength where all the absorbance lines intersect;
(c) varying the amount of Total Hardness in the fluid and measuring the absorbance of Plasmocorinth B at the wavelength of the isosbestic point and plotting absorbance versus concentration of Total Hardness as CaCO3 in ppm;
(d) preparing a standard plot of the fluorescent signal of Plasmocorinth B in the same fluid by measuring the fluorescent signal of the same fluid containing different levels of magnesium and plotting the fluorescent signal of Plasmocorinth B versus concentration of magnesium as CaCO3 in ppm;
(e) adding the same amount of Plasmocorinth B to the sample of fluid as was used in steps (c) and (d);
(f) measuring the absorbance of the Plasmocorinth B in the fluid at the wavelength of the isosbestic point; wherein the absorbance is measured after the Plasmocorinth B has interacted with soluble hardness present;
(g) measuring the fluorescent signal of the Plasmocorinth B in the fluid after it has interacted with soluble hardness present;
(h) using the measured absorbance of Plasmocorinth B and the plots of absorbance of Plasmocorinth B versus concentration to determine the total amount of soluble hardness present with said total amount of soluble hardness present being due to the existence of both calcium and magnesium; and then;
(i) subtracting the amount of magnesium present from the amount of total soluble hardness present in order to determine the amount of calcium present; wherein the amount of magnesium present is determined by comparing the measured fluorescent signal of Plasmocorinth B in the fluid with the standard plot of fluorescent signal of Plasmocorinth B versus concentration of magnesium in the fluid.
The eighth aspect of the instant claimed invention is a method of determining whether soluble hardness is calcium or magnesium comprising the steps of:
(a) providing two identical samples of a fluid that is believed to contain both calcium and magnesium;
(b) determining the wavelength of the isosbestic point of Plasmocorinth B in said fluid by measuring the absorbance of the same fluid containing the same amount of Plasmocorinth B and fixed Total Hardness while varying the relative amounts of magnesium and calcium in the Total Hardness and plotting the absorbance versus wavelength; wherein the isosbestic point is the wavelength where all the absorbance lines intersect;
(c) varying the amount of Total Hardness in the fluid and measuring the absorbance of Plasmocorinth B at the wavelength of the isosbestic point and plotting absorbance versus concentration of Total Hardness as CaCO3 in ppm;
(d) preparing a standard plot of the fluorescent signal of a fluorogenic reagent in the same fluid by measuring the fluorescent signal of the same fluid containing different levels of magnesium and plotting the fluorescent signal of fluorogenic reagent versus concentration of magnesium; wherein said fluorogenic reagent is selected from the group consisting of Acid Alizarin Violet N, Calmagite and Eriochrome(copyright) Blue Black B;
(e) adding the same amount of Plasmocorinth B to the first of the identical samples of fluid as was used in step (c);
(f) measuring the absorbance of the Plasmocorinth B at the wavelength of the isosbestic point in the first of the identical samples of fluid, after the Plasmocorinth B has interacted with the soluble hardness present;
(g) adding the same amount of fluorogenic reagent to the second of the identical samples of fluid as was used in step (d);
(h) measuring the fluorescent signal of the fluorogenic reagent in the fluid after it has interacted with the soluble hardness present;
(i) using the measured absorbance of Plasmocorinth B and the plots of absorbance of Plasmocorinth B versus concentration to determine the total amount of soluble hardness present with said total amount of soluble hardness present being due to the existence of both calcium and magnesium; and then,
(j) subtracting the amount of magnesium present from the amount of total soluble hardness present in order to determine the amount of calcium present; wherein the amount of magnesium present is determined by comparing the measured fluorescent signal of the fluorogenic reagent in the fluid with the standard plot of fluorescent signal of fluorogenic reagent versus concentration of magnesium in the fluid.